Method and Apparatus for Improving RRC Connection Procedure

ABSTRACT

The present invention provides a method for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system. The method includes steps of performing an RRC Connection procedure, and resetting or re-establishing a lower layer protocol entity for Signalling Radio Bearers (SRBs) when a cell reselection occurs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/038,049, filed on Mar. 20, 2008 and entitled “Method and apparatus for reset RLC and MAC upon cell reselection in a wireless communication system”, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for improving a Radio Resource Control (RRC) Connection procedure, and more particularly, to a method and apparatus for improving the RRC Connection procedure by correctly resetting or re-establishing a lower layer protocol entity.

2. Description of the Prior Art

Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple. Besides, one NB is responsible for controlling one or more cells, and thus a user equipment (UE) establishing connection with the network means the UE establishing connection with one cell of NB.

In LTE system, Radio Resource Control (RRC) layer of the UE merely includes two RRC states, i.e. RRC_IDLE and RRC_CONNECTED; and Radio Bearers for transmitting RRC signals, generally called Signaling Radio Bearers (SRBs), are divided into the following three types:

1. SRB0 is for exchanging RRC messages over a Common Control Channel (CCCH). Uplink (UL) and Downlink (DL) both use a Transparent Mode (TM) RLC entity,

2. SRB1 is for exchanging RRC messages and upper layer Non-Access Stratum (NAS) messages over a Dedicated Control Channel (DCCH). The UL and DL both use an Acknowledged Mode (AM) RLC entity.

3. SRB2 is for exchanging upper layer NAS messages over DCCH. The UL and DL both use the AM RLC entity.

Through use of the SRBs, the RRC layers of the UE and the network can exchange RRC messages, as a basis for radio resource settings, for completing various RRC control procedures. For example, the UE in RRC_IDLE state can establish RRC connection with the network through a RRC Connection Establishment procedure, while the UE in RRC_CONNECTED state can re-establish RRC connection with the network through a RRC Connection Re-establishment procedure.

For the above two RRC connection procedures, the RRC layer of the UE shall generate a Connection Request message (or a Connection Re-establishment Request message), and the UE shall initiate a Random Access procedure in lower layer, i.e. MAC layer, for transmitting the Connection Request message (or the Connection Re-establishment Request message) to the network over CCCH. Meanwhile, the UE can perform radio measurement for neighboring cells, and reselect to another cell when measuring results reach to cell reselection criteria, i.e. a cell re-selection occurs. Detailed operation of the above RRC connection procedures is referable in related specification and not narrated herein.

According to the current specification, when the cell reselection occurs during an ongoing RRC Connection procedure, the RRC layer of the UE would then generate a new Connection Request message (or a new Connection Re-establishment Request message) to the lower layer for transmission to a new selected cell. However, since the MAC layer is not reset and the RLC layer mapping to the SRB is not re-established as well, the Random Access procedure for an original cell is still executed, causing the Random Access procedure for the new cell cannot be correctly performed. In addition, if the Connection Request message (or the Connection Re-establishment Request message) for the original cell cannot be sent out before the cell reselection occurs, there would be two or more Connection Request messages (or Connection Re-establishment Request messages) in a transmission buffer of the RLC layer. As a result, the follow-up RRC Connection procedure cannot be completed correctly, and may cause errors, such as sending a redundant Connection Request message (or Connection Re-establishment Request message) to the new cell.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide a method and apparatus for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communications system.

According to the present invention, a method for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system is disclosed. The method includes steps of performing an RRC Connection procedure; and resetting or re-establishing a lower layer protocol entity for a Signalling Radio Bearer (SRB) when a cell reselection occurs.

According to the present invention, a communications device for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system is disclosed. The communications device includes a processor for executing a program code, and a memory, coupled to the processor, for storing the program code. The program code includes steps of performing an RRC Connection procedure; and resetting or re-establishing a lower layer protocol entity for a Signalling Radio Bearer (SRB) when a cell reselection occurs.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless communications system.

FIG. 2 is a function block diagram of a wireless communications device.

FIG. 3 is a diagram of program code of FIG. 2.

FIG. 4 is a flowchart of a process according to an embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which illustrates a schematic diagram of a wireless communications system 1000. The wireless communications system 1000 can be a 3G mobile telecommunications system, an LTE (long-term evolution) system or other mobile communications systems, and is briefly composed of a network and a plurality of user equipments (UEs). In FIG. 1, the network and the UEs are simply utilized for illustrating the structure of the wireless communications system 1000. Practically, the network may comprise a plurality of base stations (Node Bs), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc.

Please refer to FIG. 2, which is a functional block diagram of a communications device 100 in a wireless communications system. The communications device 100 can be utilized for realizing the UEs in FIG. 1, and the wireless communications system is preferably the LTE system. For the sake of brevity, FIG. 2 only shows an input device 102, an output device 104, a control circuit 106, a central processing unit (CPU) 108, a memory 110, a program code 112, and a transceiver 114 of the communications device 100. In the communications device 100, the control circuit 106 executes the program code 112 in the memory 110 through the CPU 108, thereby controlling an operation of the communications device 100. The communications device 100 can receive signals input by a user through the input device 102, such as a keyboard, and can output images and sounds through the output device 104, such as a monitor or speakers. The transceiver 114 is used to receive and transmit wireless signals, delivering received signals to the control circuit 106, and outputting signals generated by the control circuit 106 wirelessly. From a perspective of a communications protocol framework, the transceiver 114 can be seen as a portion of Layer 1, and the control circuit 106 can be utilized to realize functions of Layer 2 and Layer 3.

Please continue to refer to FIG. 3. FIG. 3 is a diagram of the program code 112 shown in FIG. 2. The program code 112 includes an application layer 200, a Layer 3 202, and a Layer 2 206, and is coupled to a Layer 1 218. The Layer 3 202 comprises a Radio Resource Control (RRC) layer, and performs radio resource control. The Layer 2 206 comprises a Radio Link Control (RLC) layer and a Medium Access Control (MAC) layer, and performs link control. The Layer 1 218 performs physical connections. Besides, the Layer 3 202 can exchange RRC messages with the network through Signalling Radio Bearers (SRBs) so as to complete various RRC procedures.

In the LTE system, when an RRC Connection procedure is performed, the Layer 3 202 shall generate a Connection Request message (or a Connection Re-establishment Request message) and a Random Access procedure in the MAC layer shall be initiated for transmitting the Connection Request message (or the Connection Re-establishment Request message) to the network over CCCH. At this time, if a cell reselection occurs, the Layer 3 202 would then generate a new Connection Request message (or a new Connection Re-establishment Request message) to the lower layer for transmission to a new cell. In such a situation, the embodiment of the present invention provides an RRC Connection improving program code 220 for accurately resetting or re-establishing a lower layer protocol entity to complete the follow-up RRC Connection procedure.

Please refer to FIG. 4, which illustrates a schematic diagram of a process 40. The process 40 is utilized for improving an RRC Connection procedure in a UE of the wireless communications system 1000, and comprises the following steps:

Step 400: Start.

Step 402: Perform an RRC Connection procedure.

Step 404: Reset or re-establish a lower layer protocol entity for an SRB when a cell reselection occurs.

Step 406: End.

According to the process 40, if the cell reselection occurs during the RRC Connection procedure performed by the UE, the lower layer protocol entity for the SRB would be reset or re-established in the embodiment of the present invention. Moreover, the step of resetting or re-establishing the lower layer protocol entity for the SRB further includes re-establishing a Transparent Mode (TM) RLC entity and resetting a Medium Access Control (MAC) entity.

Thus, when cell reselection occurs during the RRC Connection Procedure, the UE would reset or re-establish the lower layer protocol entity for the SRB so as to discard a previous RRC Connection Request message (or a RRC Connection Re-establishment Request message) and to stop an ongoing Random Access procedure. As a result, the follow-up RRC Connection procedure can be correctly completed, so as to prevent the previous Connection Request messages (or the Connection Re-establishment Request messages) from being transmitted to the new cell or prevent the Random Access procedure being performed inaccurately.

Preferably, the above RRC Connection procedure can be an RRC Connection establishment procedure or an RRC Connection Re-establishment procedure. Besides, in the embodiment of the present invention, re-establishing the TM RLC entity further includes flushing a transmission buffer of the RLC entity, so that all un-transmitted RLC Service Data Units (SDUs) in the transmission buffer can be discarded.

In summary, when the cell reselection occurs during the RRC Connection Procedure, the embodiment of the present invention resets or re-establishes the lower layer protocol entity for the SRB, so as to correctly complete the follow-up RRC Connection procedure and avoid errors.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

1. A method for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system, the method comprising: performing an RRC Connection procedure; and resetting or re-establishing a lower layer protocol entity for a Signalling Radio Bearer (SRB) when a cell reselection occurs.
 2. The method of claim 1, wherein the RRC Connection procedure is an RRC Connection establishment procedure.
 3. The method of claim 1, wherein the RRC Connection procedure is an RRC Connection Re-establishment procedure.
 4. The method of claim 1, wherein the SRB is an SRB0.
 5. The method of claim 1, wherein resetting or re-establishing the lower layer protocol entity for the SRB comprises re-establishing a Radio Link Control (RLC) entity for the SRB.
 6. The method of claim 5, wherein the RLC entity is a Transparent Mode (TM) RLC entity.
 7. The method of claim 5, wherein re-establishing the RLC entity for the SRB comprises flushing a transmission buffer of the RLC entity.
 8. The method of claim 1, wherein resetting or re-establishing the lower layer protocol entity for the SRB comprises resetting a Medium Access Control (MAC) entity for the SRB.
 9. A communication device for improving a Radio Resource Control (RRC) Connection procedure in a user equipment (UE) of a wireless communication system, the communication device comprising: a processor for executing a program code; and a memory coupled to the processor for storing the program code; wherein the program code comprises: performing an RRC Connection procedure; and resetting or re-establishing a lower layer protocol entity for a Signalling Radio Bearer (SRB) when a cell reselection occurs.
 10. The communication device of claim 9, wherein the RRC Connection procedure is an RRC Connection establishment procedure.
 11. The communication device of claim 9, wherein the RRC Connection procedure is an RRC Connection Re-establishment procedure.
 12. The communication device of claim 9, wherein the SRB is an SRB0.
 13. The communication device of claim 9, wherein resetting or re-establishing the lower layer protocol entity for the SRB comprises re-establishing a Radio Link Control (RLC) entity for the SRB.
 14. The communication device of claim 13, wherein the RLC entity is a Transparent Mode (TM) RLC entity.
 15. The communication device of claim 13, wherein re-establishing the RLC entity for the SRB comprises flushing a transmission buffer of the RLC entity.
 16. The communication device of claim 9, wherein resetting or re-establishing the lower layer protocol entity for the SRB comprises resetting a Medium Access Control (MAC) entity for the SRB. 